Background/Aims: Zinc is crucial for proper thyroid hormone metabolism; zinc deficiency may result in decreased thyroid hormone levels and resting metabolic rate (RMR). The purpose of this investigation was to assess the effects of zinc supplementation on plasma zinc, serum ferritin, plasma total triiodothyronine (T3) and thyroxine (T4), serum free T3 and T4, and thyroid-stimulating hormone concentrations, and RMR in zinc-deficient, physically active women. Methods: Two zinc-deficient female college students (ZD1 and ZD2) were supplemented with 26.4 mg/day of zinc (as zinc gluconate), and the above parameters were analyzed at 0, 2 and 4 months. Results: Zinc deficiency was clinically corrected in both subjects, while serum ferritin concentration declined to classify both subjects as borderline iron deficient (ZD1 = 15.3 and ZD2 = 15.3 ng/ml at 4 months). At 4 months, total T3 concentrations increased in ZD1, while all thyroid hormone concentrations increased in ZD2. RMR increased in both subjects by 4 months. Conclusion: Zinc supplementation appeared to be directly responsible for the increase in plasma zinc and decline in serum ferritin concentrations in both subjects. Zinc supplementation appeared to have a favorable effect on thyroid hormone levels, particularly total T3, and RMR.